Aerial imagery has vastly improved since the Wright brothers first took to the sky. Indeed, there have been many improvements in the photography and digital imaging fields.
While the earliest aerial imagery relied on conventional film technology, a variety of electronic sensors are now more commonly used. Some collect image data corresponding to specific visible, UV or IR frequency spectra (e.g., the MultiSpectral Scanner and Thematic Mapper used by the Landsat satellites). Others use wide band sensors. Still others use radar or laser systems (sometimes stereo) to sense topological features in 3 dimensions. Some satellites even collect ribbon imagery (e.g., a raster-like, 1-demensional terrestrial representation, which is pieced together with other such adjacent ribbons).
The quality of the imagery has also constantly improved. Some satellite systems are now capable of acquiring image and topological data having a resolution of less than a meter. Aircraft imagery, collected from lower altitudes, provides still greater resolution.
A vast amount of aerial imagery is constantly being generated and collected. Management of the resulting large data sets is a growing problem. In today's digital world, images are routinely manipulated, even on home computers. Management of resulting image ancestry, image derivates and related metadata is increasingly difficult.
According to one aspect of the present invention, a digital watermark-based image management system helps solve these and other problems. A digital watermark is ideally employed as an enabler to access a related family of images, linked in a database (or other data structure) via digital watermark identifiers. Watermark identifiers can also be used to identify the source of an image, track images and documents, document a distribution chain, and identify unlabeled hard copy images. According to another aspect, digital watermarks help to provide security, monitoring and gatekeeper-like functions.
Digital watermarking is a form of steganography that encompasses a great variety of techniques by which plural bits of digital data are hidden in some other object without leaving human-apparent evidence of alteration.
Digital watermarking may be used to modify media content to embed a message or machine-readable code into the content. The content may be modified such that the embedded code is imperceptible or nearly imperceptible to the user, yet may be detected through an automated detection process.
Most commonly, digital watermarking is applied to media such as images, audio signals, and video signals. However, it may also be applied to other types of data, including documents (e.g., through line, word or character shifting, through texturing, graphics, or backgrounds, etc.), software, multi-dimensional graphics models, and surface textures of objects.
The assignee's U.S. Pat. No. 6,122,403, and co-pending U.S. patent application Ser. No. 09/503,881, detail suitable digital watermarking techniques in which values of pixels, e.g., in a 100×100 pixel patch, can be slightly altered so as to convey a plural-bit payload, without impairing use of the pixel data for its intended purpose. The payload may be on the order of 2–256 bits, depending on the particular form of encoding (e.g., convolution, turbo, or BCH coding can be employed to provide some error-correcting capability), and the number of bits per pixel. Larger payloads can be conveyed through larger image patches. (Larger payloads can also be conveyed by encoding the information in a less robust fashion, or by making the encoding more relatively visible.). The watermark payload can convey an image identifier, and may convey other metadata as well. In some embodiments, the component image files are tagged both by digital watermark identifiers and also by conventional out-of-band techniques, such as header data, thereby affording data redundancy. Of course, there are many watermarking techniques known to those skilled in the art, and such may be suitably interchanged with the present invention.
Digital watermarking systems typically have two primary components: an embedding component that embeds the watermark in the media content, and a reading component that detects and reads the embedded watermark. The embedding component embeds a watermark pattern by altering data samples of the media content. The reading component analyzes content to detect whether a watermark pattern is present. In applications where the watermark encodes information, the reading component extracts this information from the detected watermark. Commonly assigned U.S. application Ser. No. 09/503,881, filed Feb. 14, 2000, discloses various encoding and decoding techniques. U.S. Pat. No. 5,862,260 discloses still others.
Watermarking may be performed in stages, at different times. For example, a unique identifier can be watermarked into an image relatively early in the process, and other information (such as finely geo-referenced latitude/longitude) can be watermarked later. A single watermark can be used, with different payload bits written at different times. (In watermark systems employing pseudo-random data or noise (PN), e.g., to randomize some aspect of the payload's encoding, the same PN data can be used at both times, with different payload bits encoded at the different times.).
Alternatively, different watermarks can be applied to convey different data. The watermarks can be of the same general type (e.g., PN based, but using different PN data). Or different forms of watermark can be used (e.g., one that encodes by adding an overlay signal to a representation of the image in the pixel domain, another that encodes by slightly altering DCT coefficients corresponding to the image in a spatial frequency domain, and another that encodes by slightly altering wavelet coefficients corresponding to the image. Of course, other watermarking techniques may be used as suitable replacements for those discussed above.).
In some multiple-watermarking approaches, a first watermark is applied before a satellite image is segmented into patches. A later watermark can be applied after segmentation. (The former watermark is typically designed so as to be detectable from even small excerpts of the original image.)
A watermark can be applied by an imaging instrument. In some embodiments, the image is acquired through an LCD optical shutter, or other programmable optical device, that imparts an inconspicuous patterning to the image as it is captured. (One particular optical technique for watermark encoding is detailed in U.S. Pat. No. 5,930,369.). Or the watermarking can be effected by systems in a satellite (or other aerial platform) that process the acquired data prior to transmission to a ground station. In some systems, the image data is compressed for transmission-discarding information that is not important. The compression algorithm can discard information in a manner calculated so that the remaining data is thereby encoded with a watermark.
A ground station receiving the satellite transmission can likewise apply a watermark to the image data. So can each subsequent system through which the data passes, if desired.
Preferably, such watermarking processes are secure and cannot be replicated by unauthorized individuals.
The foregoing and additional features and advantages of the present invention will be more readily apparent from the following detailed description with reference to the following figures.